Various electrolytic hydrodimerization processes for ethylenically unsaturated compounds in aqueous solutions have been proposed in the prior art. For example, alpha, beta-ethylenically unsaturated ketones, and unsaturated compounds such as coumarin, stilbene and acrolein have been hydrodimerized by electrolysis in aqueous medium. Various publications and patents have described the hydrodimerization of these and other compounds. For example, U.S. Pat. No.3,630,861 describes the hydrodimerization of acrylonitrile to adiponitrile. A homogeneous aqueous solution of the acrylonitrile and a quaternary ammonium salt of an oxygen-containing inorganic acid at a pH of from 5 to 10 is subjected to electrolysis in a single compartment cell to form adiponitrile with reduced formation of by-products. The electrolytic reductive coupling of hydroxy benzaldehydes is described in U.S. Pat. No. 4,087,336. The production of pinnacols by electrolytic hydrodimerization of carbonyl compounds is described in U.S. Pat. No. 3,899,401.
The electrolytic hydrodimerization of pyridinium salts is described in the prior art. For example, U.S. Pat. No. 3,627,651 describes a process for the production of 1,1'-disubstituted-4,4'-bipyridylium salt which comprises reducing electrolytically an N-substituted pyridinium salt having in the 4-position a substituent which is a good leaving group and which is capable of forming a stable anion. Examples of good leaving groups are the cyanide group or a halide group. Other patents describing the electrolytic dimerization of various N-substituted pyridinium salts are U.S. Pat. Nos. 3,717,646; 4,176,020; and 4,670,111.
U.S. Pat. No. 3,661,739 describes a method of electrochemical hydrodimerization of olefinic compounds represented by the general formula EQU CH.sub.2 .dbd.CHX
wherein X is selected from the group consisting of nitrile, ester, amide, aldehyde and carbonyl The electrolytic cell contains an anode and a cathode wherein the cathode is graphite having formed in the pores thereof, an ion-exchange polymer which is insoluble in the reaction mixture and contains tetraalkyl ammonium or a substituted tetraalkyl ammonium group.